UCPD pin protection

[Carl_G]

The UCPD / CC circuit is one of the few that connect an MCU pin to the PCB connector. There does not appear to be any specific information on how to protect this pin. Thus, I assume the same rules as other pins apply. That means 5V  or even 3V being applied to this pin when the MCU is unpowered would be bad. Is there any recommended protection scheme against this? Is an inline resistor sufficient?

[FBL]

Hi @Carl_G 

For STM32 devices integrating a UCPD peripheral, it is recommended to use a TCPP protection port on each USB‑C  USB PD port, depending on the role (sink, source, or DRP). This approach prevents violations of current injection specifications and AMRs on the STM32 pins.

[Carl_G]

I can see this based on the Nucleo boards. However, the Discovery board doesn't do this. It separates the UCPD from outside using FETs. Is there some underlying engineering criteria I need to be aware of? Or are we working with standard GPIO protections?

[FBL]

Hi @Carl_G 

Usually for discovery and eval board TCPP protections are provided on board. Here is an example. Can you specify which discovery board are you using? For older boards, you are absolutely right.

About standard GPIO protections, these are not sufficient for UCPD CC pins. These pins require specific protections like ESD and OVP. Connecting CC pins directly to connectors without proper protection can lead to reliability issues, especially in terms of electrostatic discharge ESD. You should be aware that using dedicated protection components for USB TypeC functionality is crucial to ensure reliable power supply.

[Carl_G]

STM32G071B-Disco.
I expect each pin has some limits but the reference manual does not indicate anything special above regular GPIO. So I'm asking if the GPIO maximums apply and I should follow that. I understand TCPP is available but I still want to know MCU requirements.